Diesel fuel used in internal combustion engines must be filtered before going to the fuel injection pump. Such filters tend to become clogged with a waxy material in the fuel which precipitates out of the diesel fuel at lower temperatures. It is therefore generally necessary to provide heating of the diesel fuel before it enters the filter when the ambient temperature drops below about 10.degree. C. Electric fuel heaters have been used in the past with a thermally sensitive mechanical switch being used to turn the heater on or off, depending on the temperature of the fuel. One such fuel heater arrangement is described, for example, in copending application Ser. No. 289,166 filed Aug. 3, 1981, in the name of the same inventor as the present application, now issued as U.S. Pat. No. 4,424,422. However, because thermally activated snap-acting mechanical switches are relatively expensive to manufacture, are not always reliable, and are expensive to replace, it is desirable to provide a fuel heater which does not depend on a mechanical switch for its operation.